Measurements of transition probabilities for two N I infrared transitions and their application for diagnostics of low temperature plasmas

Spectra emitted from a wall-stabilized arc, running in a gas mixture of helium, argon, nitrogen, oxygen and traces of hydrogen have been studied. Intensities of selected spectral transitions of neutral nitrogen and oxygen have been measured. Applying the Boltzmann plot method and using a reliable set of O I transition probabilities of spectral lines, originating from levels considerably spread in excitation energies, the temperatures of arc plasmas have been determined. Line intensities of two N I infrared transitions, originating from doubly excited terms 3p' 2Fo and 3p' 2G have been measured. In order to obtain the corresponding transition probabilities (Aki) for these lines, intensities of other N I infrared lines, with well known transition probabilities (taken from recently published data by Wiese and Fuhr [W.L. Wiese and J.R. Fuhr, Improved critical compilations of selected atomic transition probabilities for neutral and singly ionized carbon and nitrogen, J. Phys. Chem. Ref. Data 36 (2007) 1287-1345] from National Institute of Standards and Technology - NIST) have been measured. For evaluation of the transition probabilities the temperatures obtained from the above mentioned O I Boltzmann plots have been used. The results agree satisfactorily with older data found in literature. The new Aki values for transitions involving the doubly excited levels, together with Aki values taken from the above mentioned NIST source (used for determination of the new Aki values), are proposed as a convenient set for determining temperatures of plasmas containing nitrogen atoms.